Exoplanet discovery rate goes from a trickle to a flood

Today, NASA's Kepler team has announced that it has developed a new technique to verify the existence of many of the planetary candidates in its back catalog. The technique, which relies on the presence of multiple planets in the system, has led to the single largest announcement of new planets in history: 715 of them, orbiting a total of 305 stars. Most of these are small, between the sizes of Earth and Neptune, and are tightly packed in the inner regions of the systems in which they reside, but four appear to be in the habitable zone.

If you visit Kepler's home page, you'll see a count of confirmed planets in the upper right (it's currently at 961). Hover over it, and you'll see there are over 3,800 unconfirmed planetary candidates. Those candidates come from the method that Kepler uses to discover planets: watching for a mini-eclipse that causes a slight dimming of their host star's light. A similar pattern can be caused by a dim star orbiting in the system (a configuration called an eclipsing binary system), which raises the prospect of false positives.

In the past, this has generally involved multiple follow-up observations with a large telescope, which has held back the announcement of confirmed planets to a relative trickle. However, there have been a number of discoveries that have been based on Kepler data alone. These discoveries have come from multi-planet systems, where the planets gravitationally interacted, speeding up or slowing each other down. This activity creates regular variations in the timing and duration of the eclipses as the exoplanets transit between their host star and Earth.

The new technique takes a different approach to these orbital interactions. If the bodies interacting are as massive as stars, then the systems would be dynamically unstable; one or more of the stars would be ejected from the system. That leaves one other likely candidate for causing a false positive in these multiple-transit systems: planets orbiting some other star in the foreground. Based on the rate of these sorts of false positives and their distribution in the Kepler data, the chance of the multi-transit signals coming from a false positive works out to be about one percent—which places the probability that they're planets at a statistically significant 99 percent.

As a result, the Kepler team is now willing to call them planets and not just planetary candidates. Although there are still some hitches, as the SETI Institute's Jason Rowe referred to them as candidates during today's announcement. "I've been training myself for four years to say candidates," he said by way of excuse.

Enlarge/ The size of the far-right bar gives you a sense of how much this analysis has accelerated the pace of planet discovery.

NASA

Using the first two years of Kepler data, over 300 stars come through this statistical analysis, and they are host to 715 new exoplanets—the largest collection ever announced at once. The vast majority are in the inner regions of their exosolar systems, and the exoplanets themselves are generally small, hovering awkwardly between super-Earths and mini-Neptunes. The tight packing and large size mean that these exosolar systems have a lot more mass in their inner reaches, which suggests that either the planets have migrated inward or the star started out with a much larger planet-forming disk (or some combination of the two).

The changing picture of our planet catalog was also emphasized during the press conference, driven home by the graph below.

Enlarge/ With the new discoveries (orange), the bulk of the planets we know about is growing ever smaller.

NASA

Meanwhile, preparations for the next phase of Kepler's scientific career are continuing. Although the probe lost one of its 20 imaging sensors to a hardware failure, controllers are confident that they can gather sufficient data from the remaining 19. And initial tests of the new pointing procedure suggest that it will be able to outperform ground-based observatories despite the loss of two of Kepler's reaction wheels.

Materials from today's press call, including two papers describing the new planet-validating technique, have been placed online by NASA.

715 Planets that no rocket will ever reach in your lifetime, or your children's lifetime, or grand children's lifetime, or great grand children's lifetime, or great great grand children's lifetime, or ...

And? Discovering things that we can't actually get to doesn't lessen the wonder of the discovery. You'll never touch a dinosaur, either, but dinosaurs are still awesome to learn about.

I recommend trying each one of the 40-something symbols, rather than flying in a has-been archeologist from the ass-end of academia. There isn't THAT many combinations.

Well that would make a shitty show, now wouldn't it?

Besides, the 7th one ended up just being earth ...

What I want to know is why did the people rebelling take the time to write down the "phone number" of the people they were rebelling against. It is implied in the movie that they were stealing humans to bring to Abydos as slaves.

Sad that Kepler is at diminished capacity now. The real interesting finds were only slated to come up around now.

Kepler's method of transit detection requires effectively 3-4x the orbital period of a planet to be sure of transit detection.

The spacecraft essentially collects exoplanetary eclipses. To be relatively sure it was a planetary transit/eclipse, you have to wait until you see a second one of the same duration/size. To really be confident you need to see three of them.

For a planet with an orbital 'year' of one Earth year, you have to observe for at least three years (if you got lucky and just caught the first transit) and up to almost four years (if you got unlucky and just missed the first transit).

Kepler was only collecting data for about 4 years. Enough to catch some earth-year period planets, but not all it could have. And definitely not enough time for confidence of many many planets in the 'goldilocks' zone around their stars (but having orbital periods greater than one Earth year).

The disappointing failure of the spacecraft aside, I think Kepler did succeed in its main mission: to give us an idea of how many potentially habitable worlds there are in our galaxy. In a very big way, Kepler answered that question, and the answer is as high as most would have dared hope.

715 Planets that no rocket will ever reach in your lifetime, or your children's lifetime, or grand children's lifetime, or great grand children's lifetime, or great great grand children's lifetime, or ...

I recommend trying each one of the 40-something symbols, rather than flying in a has-been archeologist from the ass-end of academia. There isn't THAT many combinations.

Well that would make a shitty show, now wouldn't it?

Besides, the 7th one ended up just being earth ...

What I want to know is why did the people rebelling take the time to write down the "phone number" of the people they were rebelling against. It is implied in the movie that they were stealing humans to bring to Abydos as slaves.

They didn't, they just weren't smart enough to not bury it with the Stargate ... it was like if someone was trying to get rid of some bombs by burying them, but then tossed the fuses into the same hole because they thought it was a box of grenades.

715 Planets that no rocket will ever reach in your lifetime, or your children's lifetime, or grand children's lifetime, or great grand children's lifetime, or great great grand children's lifetime, or ...

Just one more reason to have my head frozen when I kick the bucket, dude. Sorry YOU won't be around for that rocket, I plan to be on it

I recommend trying each one of the 40-something symbols, rather than flying in a has-been archeologist from the ass-end of academia. There isn't THAT many combinations.

Well that would make a shitty show, now wouldn't it?

Besides, the 7th one ended up just being earth ...

What I want to know is why did the people rebelling take the time to write down the "phone number" of the people they were rebelling against. It is implied in the movie that they were stealing humans to bring to Abydos as slaves.

They didn't, they just weren't smart enough to not bury it with the Stargate ... it was like if someone was trying to get rid of some bombs by burying them, but then tossed the fuses into the same hole because they thought it was a box of grenades.

Been awhile since I watched the movie but I thought they used that stone to block the gate and then put the address on it.

715 Planets that no rocket will ever reach in your lifetime, or your children's lifetime, or grand children's lifetime, or great grand children's lifetime, or great great grand children's lifetime, or ...

And? Discovering things that we can't actually get to doesn't lessen the wonder of the discovery. You'll never touch a dinosaur, either, but dinosaurs are still awesome to learn about.

Besides, that's why we have radio. And innovation.

and with a crazy enough space telescope arrays and mirrors, we'll be surface imaging thousands of year old klingons, and i'm not talking about dicobalt's pants!

Been awhile since I watched the movie but I thought they used that stone to block the gate and then put the address on it.

It has been years for me too ..... you could be right; I thought it was just that they dumped everything that had to do with the Stargate into the same hole and walked away, but I really don't remember.

What we ought to be doing is spending money to build several Kepler-like spacecraft so that if one fails, there's backups. Now that there's no need for ground telescopes to verify the findings (that was the previous bottleneck), the rate of discovery and the answering of the "are we alone" question can proceed that much faster.

Given the political climate of the US though, I would not hold my breath.

I recommend trying each one of the 40-something symbols, rather than flying in a has-been archeologist from the ass-end of academia. There isn't THAT many combinations.

Well that would make a shitty show, now wouldn't it?

Besides, the 7th one ended up just being earth ...

What I want to know is why did the people rebelling take the time to write down the "phone number" of the people they were rebelling against. It is implied in the movie that they were stealing humans to bring to Abydos as slaves.

It's interesting to see how the number of discovered planets rises as they get larger. But the fact that there are so many earth sized found already is a good sign. It's simply easier to find larger planets, so there is a lot of room for many more smaller planets to be found out there.

In our system, small planets are 50% of the total (sorry Pluto guys). We may not be typical, but we could be. Too early to tell. But exciting nevertheless.

Hard to believe but understandable that many astronomers 25 years ago thought that there was a possibility that our solar system could be unique and that planet formation around other stars could be rare.It's exciting times even if it's unlikely that we'll ever reach any of them.

What we ought to be doing is spending money to build several Kepler-like spacecraft so that if one fails, there's backups…

This article isn't the first time I've read about reaction wheels failing on NASA space telescopes, and it's expensive to fix them in space, replace the mission or lose mission capabilities early. It would be expensive to make two Keplers, launch one and fix the second retrospectively prior to launch when the design flaws/weaknesses of the first become apparent: it's probably better that we should learn lessons from Kepler and design a new space telescope with new propulsion/sensor/semiconductor technology.Is anyone working on more reliable reaction wheels, or on patterns of reaction-wheel usage that can improve their life-span?

What are the distances to these various planets? What fraction of the sky does this number represent? Can these numbers be used to extrapolate the distribution in the galaxy?

Last year there were estimates of around three hundred billion in the milky way galaxy with the results suggesting 17 billion planets whose size more or less matches Earth's size but even that was a low estimate.

Try searching for "Planetary Census: Hundreds of Billions in the Milky Way?" on Google. You'll come across an article in the Time magazine that goes in depth on the topic.

After skimming down the list on Kepler's site, 6 planets stood out to me as "habitable" based off temperature (mid to high 200s in Kelvin).

Kepler-283cKepler-296eKepler-296fKepler-309cKepler-315cKepler-397c

Unfortunately the last three are more than twice as large as Earth (more than 4x) so I would imagine the increased gravity would kill us (assuming they're also not gas planets). The others are just under twice the size.

Just wish the site listed our distance from these planets. I know it's a pipe dream to imagine anything being sent to these other planets, let alone humans, within the remote future, but it's still cool to think about.

What we ought to be doing is spending money to build several Kepler-like spacecraft so that if one fails, there's backups. Now that there's no need for ground telescopes to verify the findings (that was the previous bottleneck), the rate of discovery and the answering of the "are we alone" question can proceed that much faster.

Given the political climate of the US though, I would not hold my breath.

The method used for this batch will only work for systems with at least 2 planet candidates orbiting a star. Systems that only have one will still need to be confirmed the conventional way.

What we ought to be doing is spending money to build several Kepler-like spacecraft so that if one fails, there's backups. Now that there's no need for ground telescopes to verify the findings (that was the previous bottleneck), the rate of discovery and the answering of the "are we alone" question can proceed that much faster.

You still need ground telescopes to verify the cases which are single-planet systems. Part of this announcement is simply a change of policy, they're decided that systems with transiting planets are rare enough that there are unlikely to be two of them in a Kepler pixel, rather than requiring observations of transit time variations that prove that the two planets have gravitational influence on one another and so must be orbiting the same star.

If you had the money to build and launch two Keplers, I think it would be more sensible to spend the second Kepler's-worth on thirty copies of the Hobby-Eberly telescope and thirty copies of the HARPS instrument, to remove the telescope-time bottleneck in verification from the ground.

This news is tremendous, when do we expect the next planet hunting mission to be launched?

TESS goes up in 2017, looking for Earth-sized planets in close orbits around nearby and bright stars across the whole sky - it uses four cameras with 250mm f/1.6 wide-format lenses, each with a 60mm-square 16-megapixel CCD array behind it.

PLATO goes up in 2024, and can find Earth-sized planets in Earth-like orbits around moderately bright stars; the expected lifetime is enough to scan half the sky. It uses 34 cameras, each of which is a 240mm f/2 ultra-wide-format lens with an 81-megapixel 150mm-square CCD array behind it.

What we ought to be doing is spending money to build several Kepler-like spacecraft so that if one fails, there's backups…

This article isn't the first time I've read about reaction wheels failing on NASA space telescopes, and it's expensive to fix them in space, replace the mission or lose mission capabilities early. It would be expensive to make two Keplers, launch one and fix the second retrospectively prior to launch when the design flaws/weaknesses of the first become apparent: it's probably better that we should learn lessons from Kepler and design a new space telescope with new propulsion/sensor/semiconductor technology.Is anyone working on more reliable reaction wheels, or on patterns of reaction-wheel usage that can improve their life-span?

Reaction wheels are actually fairly reliable (admittedly not reliable enough, but not that bad either). Additionally, they often put them into a configuration (e.g., the four sides of a pyramid) so that if one fails they still have 100% capability and if two fail they still have 100% capability in two axes but reduced capability in the third. You could add a fifth or sixth wheel, but then the control algorithms get very, very unwieldy.

Remember, these craft are not flying Haswell Core I-7 processors. Many are still running a rad hard PowerPC 750 (roughly equivalent to what was running in a Mac Pro about 15 years ago). If the quick and dirty check I did, the RAD750 is what Kepler has. As a general rule of thumb, take the processing capability the leading edge PC had 6-7 years ago and that's what would launch on a NASA craft today.

Additionally, there have been configurations of reaction wheels that have launched with such oddities as reaction wheels on tilt platforms (platforms that actually move within the satellite while in space in order to facilitate maneuvers). Such esoteric configurations add cost and complexity -- and complexity just gives more possible modes for failure.

Further, there is a lot of time, money and effort going into making reaction wheels more reliable. There have been a lot of craft that have had problems due to reaction wheels ranging from commercial communications satellites such as Anik E1 to military satellites such as those in the GPS constellation. There are real issues with constantly moving mechanisms in space environments. Things are much better than they were, but they're getting there.